mbmb451b_glycogenmet

mbmb451b_glycogenmet - Glycogen Metabolism Glycogen...

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Glycogen Metabolism Glycogen Breakdown Glycogen Synthesis Control of Glycogen Metabolism Glycogen Storage Diseases
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Glycogen Glycogen - animal storage glucan 100- to 400-Å-diameter cytosolic granules up to 120,000 glucose units α (1 6) branches every 8 to 12 residues muscle has 1-2% (max) by weight liver has 10% (max) by weight ~12 hour supply Although metabolism of fat provides more energy: 1. Muscle mobilize glycogen faster than fat 2. Fatty acids of fat cannot be metabolized anaerobically 3. Animals cannot convert fatty acid to glucose (glycerol can be converted to glucose)
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Glycogen Breakdown Three enzymes: glycogen phosphorylase glycogen debranching enzyme phosphoglucomutase Glycogen phosphorylase ( phosphorylase ) - phosphorolysis of glucose residues at least 5 units from branch point Glycogen + P i glycogen + glucose-1-phosphate (n residues) (n-1 residues) homodimer of 842-residues (92-kD) subunits allosteric regulation - inhibitors (ATP, glucose-6- phosphate, glucose) and activator (AMP), T R covalent modification (phosphorylation) - modification/demodification phosphorylase a ( active , SerOPO 3 2- ) phosphorylase b ( less active , Ser) narrow 30-Å crevice binds glycogen, accommodates 4 to 5 residues Pyridoxal-5-phosphate (vit B 6 derivative) cofactor - located near active site, general acid-base catalyst Rapid equilibrium Random Bi Bi kinetics
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Glycogen Breakdown Glycogen debranching enzyme - possesses two activities α (1 4) transglycosylase (glycosyl transferase) 90% glycogen glucose-1-phosphate transfers trisaccharide unit from "limit branch" to nonreducing end of another branch α (1 6) glucosidase 10% glycogen glucose Debranching activity < phosphorylase activity
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Glycogen Breakdown Phosphoglucomutase - a phosphoenzyme (Ser) reaction similar to that of phosphoglycerate mutase formation of glucose-1,6-bisphosphate (required for full activity) phosphoglucokinase - provides product glucose-1-phosphate + ATP glucose-1,6-bisphosphate
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Thermodynamic considerations phosphorylase reaction: G˚' = +3.1 kJ . mol -1 G = 0 when [P i /glucose-1-phosphate] = 3.5 under physiological conditions [P i /glucose-1-phosphate] ~ 30 to 100 G˚' = -5 to -8 kJ . mol
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This note was uploaded on 05/05/2011 for the course BIOL 400 taught by Professor Dr.biology during the Spring '11 term at University of Tennessee.

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mbmb451b_glycogenmet - Glycogen Metabolism Glycogen...

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